1. Field of the Invention
The present invention relates to an optical scanning device employing a laser beam utilizable in a laser printer, laser facsimile, digital copying machine, etc.
2. Description of the Related Art
An electrophotographic process has been developed as a simple and high-quality printing process in recent years, and an optical scanning device is conventionally known as a device capable of realizing this process. For example, a post-objective type of optical scanning device has such a structure that a collimator lens, an imaging lens, and a cylindrical lens are sequentially located on an optical path of a laser beam emitted from a semiconductor laser diode; that a plurality of reflecting surfaces of a polygon mirror rotatably supported by a drive motor are located on an optical path of the laser beam transmitted through the cylindrical lens; that a correcting lens is located on an optical path of a horizontal scanning light beam from the polygon mirror; and that a surface to be scanned that is movable in a vertical scanning direction of a rotatable photosensitive drum is located on an optical path of the light beam transmitted through the correcting lens.
In order to improve the optical characteristics of such an optical scanning device, it is necessary to position various optical components with a high accuracy. In an optical scanning device disclosed in Japanese Patent Laid-open No. Sho 63-210807, for example, a light emitting unit having a semiconductor laser diode, a collimator lens, etc. integrated together, a drive motor for rotatably supporting a polygon mirror, a reflecting mirror, a correcting lens, etc. are mounted in a single, flattened box-shaped housing.
The above-mentioned optical scanning device disclosed in Japanese Patent Laid-open No. Sho 63-210807 will now be more described. To prevent interference of the light emitting unit with the optical path of the horizontal scanning light beam from the polygon mirror, the light emitting unit is located aside the polygon mirror. The light emitting unit is designed so that the optical path of the horizontal scanning light beam from the polygon mirror is deflected by the reflecting mirror to emerge out of the housing. Accordingly, a surface to be scanned of a photosensitive drum is located under the housing. In this optical scanning device, the tilt of the reflecting surfaces of the polygon mirror is corrected by the correcting lens. To correct the tilt, the laser beam must be imaged in the vertical scanning direction on the reflecting surfaces of the polygon mirror, and this imaging of the laser beam is realized by the cylindrical lens. However, a focal position of the cylindrical lens possibly displaces from the reflecting surfaces of the polygon mirror in actual because of a component difference in astigmatism of the semiconductor laser diode, optical characteristics of the collimator lens, etc.
As means to eliminate such an error and image the laser beam on the reflecting surfaces of the polygon mirror by using the cylindrical lens, there has been disclosed an optical scanning device in Japanese Patent Laid-open No. Hei 4-75015, for example. In this optical scanning device, a lens holder having a cylindrical lower surface is slidably disposed in a V-shaped groove formed on an upper surface of a base, and a cylindrical lens is mounted upright on an upper surface of the lens holder in such a manner that the direction of an optical axis of the cylindrical lens coincides with the direction of sliding movement of the lens holder. Accordingly, the cylindrical lens and the lens holder are supported together slidably in the direction of the optical axis and are set at a proper position.
The above-mentioned optical scanning device in the related art have the following problems. In the former optical scanning device disclosed in Japanese Patent Laid-open No. Sho 63-210807, the various optical components are mounted commonly in the single housing to thereby effect high-precision arrangement of the various optical components and improve the optical characteristics. However, the following problems arise.
Firstly, as the various optical components are mounted in the flattened box-shaped housing having a large plan area, the housing is easily deformed because of a manufacturing error, aged change, temperature depending expansion/contraction, etc., and the deformation of the housing causes a reduction in position accuracy of the optical components to deteriorate the optical characteristics.
Secondly, as the light emitting unit is located aside the polygon mirror in order to prevent interference with the optical path of the horizontal scanning light beam, the arrangement of an optical system is not symmetrical with respect to a center axis of the optical path of the horizontal scanning light beam, thus complicating the structure of the optical system to reduce the productivity.
Thirdly, to improve the optical characteristics of the horizontal scanning light beam incident on the surface to be scanned in the optical scanning device, it is desirable to adjust the positions of the various optical components individually in mounting them into the housing. However, in the structure that the various optical components are mounted in the single, flattened box-shaped housing, it is sometimes difficult to locate adjusting optical equipment in the housing. Accordingly, the adjustment of the optical components is difficult to reduce the productivity.
Fourthly, while such an optical scanning device is incorporated in an electrophotographic apparatus in actual use, there is a possibility of an error in relative position between the optical scanning device and a surface to be scanned as of a photosensitive drum incorporated in the electrophotographic apparatus independently of the optical scanning device. In this case, since it is difficult to adjust the position of the photosensitive drum around which a developer, a charger, etc. are arranged, the position of the optical scanning device is adjusted in general. In the optical scanning device disclosed in Japanese Patent Laid-open No. Sho 63-210807, however, the housing is flattened in shape and large in plan area, and it is connected to a frame of the electrophotographic apparatus at a plurality of positions. Accordingly, the adjustment of the position of the optical scanning device is very troublesome to cause a reduction in productivity of the electrophotographic apparatus.
On the other hand, in the latter optical scanning device disclosed in Japanese Patent Laid-open No. Hei 4-75015, the laser beam can be imaged on the reflecting surfaces of the polygon mirror by using the cylindrical lens adapted to be slid and positioned even when there occurs a component difference in astigmatism of the semiconductor laser diode, optical characteristics of the collimator lens, etc. However, the following problems arise.
Firstly, the mechanism of slidably mounting the cylindrical lens holder upright holding the cylindrical lens on the V-shaped groove formed on the upper surface of the base is complicated in structure to hinder the improvement in productivity of the optical scanning device.
Secondly, the mechanism of slidably supporting the cylindrical lens in the direction of the optical axis requires a structure that a portion for permitting the sliding movement of the cylindrical lens is so formed as to be elongated in the direction of the optical axis in order to ensure a good accuracy in positional adjustment of the cylindrical lens. However, as the mechanism of slidably supporting the cylindrical lens in the direction of the optical axis is large in size to hinder a reduction in size and weight of the optical scanning device as a whole and also to render difficult the arrangement of the collimator lens or the like near the cylindrical lens in the direction of the optical axis.